Contemptuous smile (5)
I believe the answer is:
sneer
'contemptuous smile' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sneer that I've seen before include "Show contempt by contorting the face" , "Be derisive; Sheridan's Critic" , "Curl one's lip" , "Contemptuous expression" , "Taunt" .)